As is well known, a plasma is an ionized gaseous discharge which includes free electrons, charged ions and neutral species which are sometimes referred to simply as neutrals. It is also well known that, depending on the particular constituents of the plasma, a plasma can be used either to etch a substrate surface or to deposit material onto the substrate surface. Present methods for plasma etching and plasma deposition, however, have some shortcomings.
Insofar as plasma etching and plasma deposition are concerned, certain physical characteristics of a plasma are of particular importance. Firstly, it is basic knowledge that the velocities of free electrons in a plasma, greatly exceed the velocities of charged ions. It is also known that particulates can form from negatively charged species in a plasma. Further, it is known that a magnetic field has a significant effect upon free electron transport in the plasma. Specifically, plasma flux in a direction perpendicular to the magnetic field is significantly inhibited. With the above in mind, certain phenomena should be considered.
If there is no control over the flux of the faster moving free electrons in a plasma, the free electrons will leave the plasma. Accordingly, the plasma will tend to become positively charged. This condition, in turn, promotes the formation and retention of negatively charged particulates in the plasma. These particulates, however, undesirably degrade the quality of the deposition or etching on the substrate surface. Another problem stems from the fact that if the plasma is not somehow insulated from the surface of the substrate, the substrate can become overheated and, thereby, possibly damaged. This becomes even more troublesome when high plasma densities are achieved.
In addition to merely generating a plasma, an efficient plasma etching or plasma deposition system needs to have a control over the functioning of the system. Stated differently, it is desirable if the system operator is able to control independently the flux of positive ions and neutrals toward the substrate surface to be altered. Further, it is obviously desirable if the surface is predictably altered. The implied consequence of this is that the plasma needs to have a uniform density over the substrate surface that is to be altered. Finally, it is desirable that the system be responsive and able to function in a short period of time.
In light of the above it is an object of the present invention to provide a system for processing a plasma to alter the surface of a substrate having a large surface area. Another object of the present invention is to provide a system for processing a plasma to alter the surface of a substrate which can etch the surface of a substrate, or deposit material onto the surface of a substrate, at a relatively high speed. Still another object of the present invention is to provide a system for processing a plasma to alter the surface of a substrate which can control the flux of ions or neutrals from the plasma toward the surface of the substrate. Another object of the present invention is to provide a system for processing a plasma to alter the surface of a substrate which produces a beam-like ion flux into the substrate so that deep trenches can be cut into the substrate. Yet another object of the present invention is to provide a system for processing a plasma to alter the surface of a substrate which inhibits the unwanted formation of particulates in the plasma. Another object of the present invention is to provide a system for processing a plasma to alter the surface of a substrate which allows for the generations of a plasma having a uniform density. Still another object of the present invention is to provide a system for processing a plasma to alter the surface of a substrate which shields the substrate from a high electric field. It is also an object of the present invention to provide a system for processing a plasma to alter the surface of a substrate which is relatively easy to manufacture, is easy to use and comparatively cost effective.